1. Field of the Invention
This invention relates to a semiconductor light emitting device and a wafer.
2. Background Art
A near-ultraviolet LED (light emitting diode) device (emission wavelength being 400 nm or less) based on a nitride semiconductor is expected to serve as a light source for use in a white LED, but has the problem of low optical efficiency. As opposed to LD (laser diode), the emission efficiency of an LED device does not exceed the emission efficiency of its light emitting section. To increase the emission efficiency of the light emitting section, attempts have been made to fabricate a device based on a GaN substrate with low dislocation density. However, this is not a widely available technique because of its high cost in addition to low efficiency.
Conventionally, it has been considered that the low emission efficiency of an ultraviolet LED device is caused mainly by the large number of crystal defects such as dislocations in the light emitting layer. In this context, a growth technique is developed, in which a GaN layer is formed on a sapphire c-plane substrate via a buffer layer formed from high Al composition AlGaN or AlN by high-temperature growth. This technique can reduce the dislocation density to 108-109 m−3, which is lower by 1/10 or less than conventional. However, near-ultraviolet LED devices based on this technique also have room for improvement.
Japanese Patent No. 2713094 discloses a technique for increasing emission efficiency using a double heterostructure in which an n-type gallium nitride-based compound semiconductor layer serves as a first cladding layer, an InxGa1-xN layer doped with a specific amount of Si serves as a light emitting layer, and a p-type gallium nitride-based compound semiconductor layer doped with a specific amount of Mg serves as a second cladding layer.